Officials on the sidelines of the Middle East peace summit here reacted warily to the vow, reportedly made to Russian President Vladimir Putin during his landmark trip to North Korea.

"I would remind you that the North Koreans demonstrated ballistic missile capability with what they called a space or satellite launch," one official said, referring to Pyongyang's 1998 firing of a missile over Japan.

The United States and other nations expressed deep concern over the test of the Taepodong I missile, but North Korea insisted their fears were misplaced as the device had merely put into orbit a satellite emitting revolutionary songs.

State Department spokesman Adam Ereli said the United States needed to see clear evidence that North Korea was serious about ceasing missile production.

"We look forward to concrete action by North Korea on its missile program to achieve real progress in addressing the concerns of the international community," he said.

The United States made its position on the program clear during talks between Assistant Secretary of State for non-proliferation Robert Einhorn and North Korean officials in Malaysia this month, he said.

"What's important are concrete actions and we are looking forward to scheduling another round of talks to continue to discuss the proposals and ideas we put on the table in our previous round," Ereli told reporters.

White House spokesman Joe Lockhart said a detailed US reaction to the pledge would have to wait until it could be fully analyzed.

"Obviously, we have done a lot of work on that front -- on the North Korean missile program, but let me get a chance to look at that report, before I comment any further," he said.

Earlier Wednesday, the Interfax news agency quoted Putin as saying the North Koreans had vowed to give up the missile program in exchange for rocket boosters.

"North Korea on the whole is ready to use exclusively other nations' rocket technologies, if it receives rocket boosters for peaceful space exploration," Interfax quoted Putin as saying in Pyongyang.

Putin stressed nations other than Russia would be responsible for making sure North Korea received rocket boosters that could be put to commercial and scientific space use.

"We think that Russia's efforts in this alone are not enough," the ITAR-TASS news agency quoted Putin as saying.

"Everyone, including the Democratic People's Republic of Korea, South Korea, as well as the United States, China and Japan should support this process."

Putin's statement came after two-hour long talks with North Korean officials on the first day of a two-day visit to Pyongyang, the first ever by a Russian head of state.

North Korea's missile program has been cited by officials here as a primary justification for a proposed national missile defense scheme, currently in the early stages of development.

Strategists here fear North Korea will soon be capable of hitting US territory with one of its missiles, and have accused Pyongyang of funneling missiles to potential US enemies.

As Putin visited North Korea, US and North Korean officials sat down for a new round of talks in Berlin Wednesday, focusing on a wide range of issues, a State Department official said.

Ambassador Charles Kartman of the United States met a delegation headed by Kim Gye Gwan of North Korea for two days of talks, the official said.

The US and North Korea last met for talks on general issues in Rome in May, before the historic summit between North and South Korea last month.